Disadvantageous against Kagero (hard to have full rearguards for maximum power). Better if Counterblast can call any unit(not limited to Grade 2).

The reason that its limited to 2 is for cards like Gigatech Charger (Grade 3, when its placed on a vanguard circle or rear guard circle you reveal the top card of your deck and if its a royal paladin call it to rear guard), get two spots filled for the price of one.